This invention relates to flow control of liquid compositions.
In many applications for adhesives it is necessary, or highly desirable, to place the adhesive on a vertical or inclined surface prior to bonding another material to such surface. Similarly, when using various types of sealants, it is necessary to place the sealant on a vertical or inclined surface. There are many instances of this in building construction and manufacturing operations. However, when placing liquid adhesives, or sealants, on vertical or inclined surfaces, the adhesives either flow off or sag considerably before a material can be bonded to the surface by means of the adhesive, and liquid sealants tend to flow off or sag considerably before they become cured.
Although there are adhesives and sealants available which are not in liquid form, the liquid adhesives and sealants are generally preferred for many applications because they wet out the surfaces of the materials to which they are to be adhered, thereby promoting very good adhesion.
Various techniques have been used previously in order to thicken liquid materials or to suspend particulate matter such as fillers. For example, a common technique involves addition of small particle inert fillers (such as clay, talc, fumed silica, asbestos and the like) in order to thicken or body a liquid composition (such as an adhesive or sealant). The use of such fillers relies upon particle-particle interaction. There are many inherent disadvantages associated with the use of such fillers.
Although such fillers do impart thixotropy to a liquid composition, the viscosity of the composition often does not increase rapidly after shearing forces are removed. Furthermore, the fillers must be intimately mixed or compounded with the other ingredients in the composition and this requires use of a significant amount of energy. It is also possible to under-mix or over-mix such compositions; accordingly, the degree of mixing must be carefully controlled.
Moreover, such fillers may be leached out of the composition, or break down, on exposure of the composition to the environment during use. Also, some of such fillers have only specific application, i.e. not all of such fillers are useful in all types of compositions. Additionally, the effectiveness of some fillers may be negatively affected by the presence of other ingredients. Furthermore, it is often difficult to obtain the proper color desired for the ultimate composition, and it is extremely difficult, if not impossible, to obtain clear compositions having the desired properties. Fibrous fillers (such as asbestos) also tend to impart a grainy consistency to a composition, and the use of some of such fibrous fillers constitutes a serious health hazard.
Another type of additive which is often used to thicken materials such as oils and greases is a metal soap (i.e. a metallic salt.) However, such soaps may be reactive with many types of curable compositions and accordingly such soaps would tend to interfere with the curing of the composition and would therefore detract from the cured properties of the composition. Furthermore, the compositions which are bodied with such soaps are quite shear sensitive.
Another type of material which has been promoted as a thickener for liquid compositions is that commercially available from NL Industries under the "Thixcin" series. Such materials have pendent hydroxyl groups and accordingly rely upon the effects of hydrogen bonding to impart thickening characteristics. However, such materials do not operate efficiently in the presence of polar solvents. Furthermore, compositions containing such materials are very shear sensitive.
A specific technique for thickening comprising synthetic elastomer and elastomer solvent is described in U.S. Pat. No. 3,622,534. The technique described there involves the formation of urea (by reaction of an aliphatic amine with an isocyanate in the presence of the synthetic elastomer and elastomer solvent). However, no crosslinked polymer matrix is obtained. As explained in more detail hereinafter, the compositions of the present invention require the presence of a crosslinked polymer matrix.